If all the base parts are new, why are only the two front plugs giving trouble? The only place that could occur is at the distributor cap, the only place the spark goes to each seperate plug. I'd change it and see.
Though!! I had a similar problem on one of my Dodges, the cables on two plugs had touched and were fusing together, check the lines are seperated, but I'd still change the Dizzy Cap.